The present invention relates generally to semiconductor integrated circuits and methods of operating semiconductor integrated circuits, and more particularly to technology effectively applicable to EPROM (Erasable & Programmable Read Only Memory) from which data can be read at low operating voltage and what permits any general purpose writer to write data thereto.
As nonvolatile memory units, there are EPROMs from which stored data can be erased under ultraviolet rays. Data is written by a programmer (writer) to EPROM and erased by the irradiation of ultraviolet rays. EPROM has been designed to operate at a supply voltage of 5 V. When an existing general purpose writer is fitted to EPROM for the purpose of writing data, a supply voltage of 5 V to 6 V is supplied from the general purpose writer to the EPROM and a high voltage for writing is also supplied from the general purpose writer to the EPROM. Japanese Patent Laid-Open No. 108594/1988 discloses an exemplary EPROM having a circuit for appropriate writing operations to be performed by detecting such a high voltage for writing.